The present invention relates generally to the manipulation of microballoons, and more particularly to an apparatus for removably holding a plurality of microballoons in order to more efficiently carry out the filling of the microballoons with a known quantity of gas.
Glass microballoons filled with various gases are used for laser fusion targets in order to facilitate diagnosis of laser-target interaction by x-ray or radiochemical techniques and for shock-wave diagnostics. Such microballoons are currently filled with gases of interest by first perforating the microballoon with focused, high-intensity laser radiation, applying an uncured epoxy over the hole, and loading the microballoons into a pressure vessel which is first evacuate and then filled with the gas or gas mixture of interest, and finally heated for several hours to cure the epoxy. That is, the gas invades the microballoon while the epoxy is curing and cannot readily escape once the epoxy cures. Since it has been observed that permeation of the gas occurs through the glass walls of the microballoons or through the cured epoxy occurs, it is important to nondestructively measure the gas pressure inside the microballoons as close to their time of use as is possible. One successful technique for accomplishing this purpose involves the use of interferometry.
In "Measurement of Laser Fusion Capsules Using the Interferometer Method of Excess Fractions" by Roger R. Stone et al., Lawrence Livermore Laboratory Report UCRL-77487 (1975), the author describes an interferometric method of nondestructively determining the gas pressure inside of gas-filled microballoons using an interferometric technique. It is critical to the measurement that the interferometer "view" the microballoon from the identical perspective in both the unfilled and the filled configurations in order that the gas located inside of the microballoon give rise to a change in the interferometric pattern of the gas plus microballoon which can be related to the pressure of that gas therein. Additionally, the process of producing individual gas-filled microballoons is described in "Laser Fusion Targets Containing Gas Not Permeable Through A Wall: A Technique For Fabrication," by S. Butler and B. Cranfill Jorgensen, LA-UR-79-2468 (1979). However, requirements for thousands of microballoons has necessitated the development of more efficient procedures for handling and processing microballoons.